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Interpreting Seismograms
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Wave Types
P waves (compression waves)Fastest
S waves (transverse waves)Mid Speed
Surface waves Slowest, may not reach far from epicenter
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Review
• Do we feel every earthquake that happens in the world?
• Do mechanical waves generated by earthquakes reach our location?
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How do geologists know that a major earthquake occurred on the other side
of the world?
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DETECTING EARTHQUAKES
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Seismometer
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RECORDING EARTHQUAKE EVENTS
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Seismograph
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Seismogragh reading
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Measuring an earthquake at a distance
Seismographs-sensitive machines that record the different types of seismic waves generated by an earthquake
Measuring the difference between the arrival times of different types of waves indicates how far away the epicenter is from the seismograph machine
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What information can be gathered from a seismograph reading?
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ARRIVAL TIMES FOR DIFFERENT WAVES
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Determine distance to epicenter
• The difference in time between arrival of the P and S wave can be used to determine distance between epicenter and seismograph
• The bigger the difference, the greater the distance
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Seismograph reading
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Why can’t the difference between waves give the distance but not
direction to epicenter?
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WHAT IS NEEDED TO DETERMINE THE EPICENTER OF AN EARTHQUAKE?
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• Seismograph readings from instruments in 3 different locations
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Finding the epicenter
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Other uses for Seismic waves
• Used to gather data on the interior structure of the earth
• S-waves do not go through __________ material.
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A cross sectional map using info from seismic waves
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Locations of different earthquakes over the last 20 years
• Usgs program
• Show large quakes• Show shallow quakes
• Look for patterns
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World Earthquakes
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Volcanoes and Earthquakes
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Ring of Fire
• Location
• Significance?
• Atlantic ocean• Mediteraanen• East Africa
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